The present invention relates generally to tracking control systems in magnetic reproducing apparatuses, and more particularly to a tracking control system which controls the tracking of a rotary head on a track of a magnetic tape so that the rotary magnetic head finely follows and traces the track on the magnetic tape regardless of the bends in the tracks.
Magnetic recording and/or reproducing apparatuses (hereinafter referred to as VTRs) which record and/or reproduce video signals in oblique tracks on the magnetic tape by use of a rotary magnetic head, has been in wide practical use. Moreover, in order to extend the recording and/or reproducing time of the VTR for home use, by using a magnetic head with a narrow track width and reducing the tape travelling speed into one-third the normal speed, for example, a VTR constructed to perform six hours of recording and/or reproduction, which is three times the length of the normal recording and/or reproducing time of a cassette tape for performing two hours of recording and/or reproduction, has been put into practical use. In this type of VTR, there exist some degradation in the signal-to-noise (S/N) ratio compared to the two-hour recording and/or reproduction, however, six hours of recording and/or reproduction can be obtained having enough practical S/N ratio.
When recording and/or reproduction is performed for a long time by reducing the track pitch and the like, the recording and/or reproduction is easily affected by the track error as compared to normal recording and/or reproduction in which the track width and track pitch are large, and it is essentially required to obtain accurate tracking.
Therefore, the size, angle, and the like of the tape driving system mechanism differ according to the magnetic recording and/or reproducing apparatus, and in reality, there are some variations in the tape driving system. The variations in the size and shape of the tape guiding groove formed in the fixed guide drum, mounting height and mounting angle of the tape travelling guide pole, the mounting location and mounting angle of the fixed guide drum, and the like are the main reasons for the above variation in the tape driving system mechanism. Accordingly, when a magnetic tape which has been recorded by one VTR is reproduced by another VTR, bend is relatively introduced in the track on the magnetic tape with respect to the scanning locus of the rotary magnetic head. When this kind of bend in the track exist, the rotary magnetic head introduces tracking error. Furthermore, when variations exist in each VTR for the length between the position where the rotary magnetic head makes contact with the magnetic tape and the control head where the recording and/or reproduction of control signals on the tape are performed, along the length of the tape travelling path, tracking error is also introduced. When the above described tracking error exist, reproduction having good S/N ratio cannot be obtained.
Conventionally, as a system for compensating and controlling the above tracking error, a system exists in which tracking compensation is performed by using a head moving mechanism which varies the height position of the rotary magnetic head by a control signal, swings the head during the tracing period of each track by applying a constant frequency signal of 480 Hz, for example, to the head moving mechanism, detects the tracking error quantity and the shift direction by the variation in the reproduced signal level, and obtains a control signal from the detected result thus obtained and feeds back this control signal to the head moving mechanism.
However, in the above conventional system, the head is swung several times during scanning of each track by the head and suffered disadvantages in that the level variation in the reproduced signal is large. Furthermore, when this system is applied to a so-called azimuth recording and/or reproducing system in which recording and/or reproduction is performed by use of a pair of heads comprising gaps having azimuth angles of mutually opposite directions, defect is introduced in which color unevenness is introduced by the time axis variation accompanied by the swinging of the heads, since the head gaps form a certain angle with respect to the swinging direction of the heads. Moreover, since the tracking error compensation is successively performed during scanning of one track in this system, accurate tracking compensation cannot be performed when the responding operation of the above head moving mechanism is slow, and suffered such disadvantages in that the tracking error can be increased rather than be reduced.
The present inventor has conceived about the bend in the track, and found that the track bend does not differ at each track, and that bend is introduced in common at each adjacent track due to the variety of variations in the tape driving system of each of the above recording and/or reproducing apparatus. Hence, a track bend identical to that existing at a part of a tape which is a certain distance from the edge of the tape of a certain track, is introduced at a part which is a certain distance from the edge of the tape as the above, throughout the whole distance in the tape longitudinal direction. Accordingly, the present inventor perceived on this point.